Finally got around to hooking up a mic under the hood to capture the strange sound my car makes between 1500-2500 rpms. Before or after that range it's silent. You'll hear it in the audio clip- I even purposely modulate the throttle to exaggerate the sound starting and stopping.

Rob said it sounds like something rotating- possibly a pulley/bearing. Anyone else care to speculate. Thanks in advance.

http://www.gmelliottvideo.com/srt6noise.wav

 

whoa. that sounds strange.... i stay away from pulley upgrades.

hopefully it's nothing to serious.

 

Sounds like something is rubbing. Check your belt, hoses, wires everything to see if something isn't back on right. It's there from start up. Do the hose trick and try to centralize the noise.

 

Are you talking about that thunk thunk that sounds like the tread of a tire flapping? I hear several noises that I can't identify. I could be a bearing but which one and why now? I would be exploring with a listening device to eliminate parts and pieces first and then remove the belt and check all the pulleys one by one. You may be able to tell spinning them by hand. (long shot) Sorry, I really don't know.

Les

 

It sounds more like a resonance echo. Check for something moving against the intake tubes, or the hook up in the catch can, with the tubes look for vacuum leaks around the tubes where the rubber boots are. Doesn't sound like a pulley to me.

 

Sounds like a really old song from the 60's called "Echoes" by Pink Floyd

 

the noise was there before the latest big round of mods so all those can be ruled out, glen i just snet ya an email with a bunch of picture to get started with the diagnostics. can u get the noise at that rpm while in park? if so have someone sit in th ecar and hold the gas there while your under the hood checking around.

 

Unfortunately no- it only does it while in drive between those aforementioned rpms.

I appreciate all the help and input everyone.

 

Perhaps as the system is building up PSI - enough pressure is made and a leak is occuring. As PSI bleeds - the sound goes away and the cycle begins again.

There have been a few VIDs of folks having pulley/bearing issues and you can hear the grinding through the entire RPM range - your sound seems to start after the SC engages and has some time to build PSI. Just a thought.

With the car parked and at idle - spray liberal amounts of carb cleaner around the plenums flanges and listen for a change in RPM - one way to detect a leak..

 

[quote=BrianBrave]Perhaps as the system is building up PSI - enough pressure is made and a leak is occuring. As PSI bleeds - the sound goes away and the cycle begins again.

There have been a few VIDs of folks having pulley/bearing issues and you can hear the grinding through the entire RPM range - your sound seems to start after the SC engages and has some time to build PSI. Just a thought.

With the car parked and at idle - spray liberal amounts of carb cleaner around the plenums flanges and listen for a change in RPM - one way to detect a leak..[/quote

Great mind right here folks.

 

I used the carb cleaner spray back in the early 70's. It's a time proven technic for vacumn leaks. Don't see that it would be effective for finding pressure leaks. Just my thoughts! But,Is it harmless to the teflon coatings of the NeedsWings Mani's? Squirrel Crusher

 

the sound was there for you on the stock intake manifolds and stock gaskets before you install the new stuff, installing the new stuff made no change it that noise, i wouldnt spray your pretty new manifolds with brake cleaner as it will dull the finish.

loosen the belt and spin as many pulleys as you can by hand and see if you feel anything out of the ordinary

 

If your SRT6 is in park and the engine at idle, then the supercharger is not engaged and the manifold/plenums will be under vacuum. Your boost gauge will confirm this.

If the finish is damage sensative to carb cleaner or other sprays, you can use a more risky procedure with propane from a cutting / brazing torch - or a BBQ Lighter (not lit of course) - same results but with greater risks from spark......

Let us know what you discover....

 

Thanks Brian for the tip that the supercharger want engauge in park while running up the RPM's. Squirrel Crusher

 

An automotive stethiscope would come in handy to find this. Another old school trick is get a really big screw driver and place the handle to your ear while touch the metal end in suspect areas. when you find the source it will be very loud in your ear. This is also an easy way to find a worn pulley bushing. It does sound a little like the clucted s/c pulley but you also have one if these on the a/c compressor as well.

 

These are all good suggestions however keep in mind the sound only starts at 1500 rpms and fades away after 2500 rpms. This makes it much harder to isolate the noise considering it only happens when the car is in gear and moving.

I'll have Chris's brother try what Rob suggested when it's in his shot to get the Super Cooler installed. If, for the sake of argument it's a bad idler pulley from the ASP 178mm kit how would I go about replacing it? TIA

 

Email ASP, they helped lotus with his. They emailed me back right away and said they have never had one fail. lotus' idler idler bearing was completely rusted. Or just replace the bearing. You can also get a smaller belt and see if you can reroute one pulley at a time to see which if any eliminate the noise.